We have observed that the ATPdependent shape change and ATPase activities of purified erythrocyte membranes are altered by lectin binding to the seral face of the membrane. These changes occur independently of changes in cAMP, cGMP or Ca2 ion levels. If, as it appears, the effects are caused by the aggregation of membrane glycoproteins or glycolipids, then specific antibodies to erythrocyte membrane components should produce similar changes in membrane activities. Antisera to erythrocyte blood group antigens (A,B,H,I,D,K, S,M and N) and to fractions of membrane component 3 (the presumed anion channel) will be screened for their effects on shape change and ATPase activities. Purified gamma globulins from antisera which alter membrane activities will be used to establish if crosslinking is required and to study the molecular bases of the changes. Of particular interest are the effects of site density and mobility on the modulation of the ATPase and shape change activities by multivalent proteins. We also wish to understand the significance of the observations that the maximum inhibition or stimulation of membrane activities occurs when only a small fraction of the lectin binding sites are occupied and that trypsinization of the intact red cell abrogates the lectin effects without altering lectin binding in certain cases. There is evidence that membrane ATPases in other cells are altered by lectins. We plan to extend those observations on purified membrane fractions and to determine if the ATPase activity changes relate to changes in cell function. Since little is known about the molecular basis of the Mg2 ion ATPase activity which is altered by the lectins, we will attempt to purify and characterize the ATPase enzyme complex. We wish to find the function of this enzyme and to understand the mechanisms of controlling it.